Meiosis‐Reinitiation‐Inducing Factor of Tetrahymena Functions Upstream of M‐Phase‐Promoting Factor

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Abstract
Reinitiation of meiosis (maturation) of amphibian Bufo and Xenopus oocytes can be induced if Tetrahymena extract is injected into them. The activity differed from M‐phase‐promoting factor, because action of the former factor on the induction of maturation was inhibited by treatment of the oocytes with cycloheximide. Activity of M‐phase‐promoting factor was not detected in Tetrahymena extract regardless of the presence of cdc2 homologues in the extract. However, cycloheximide‐resistant‐maturation‐inducing activity appeared in the recipients, when the maturation was induced by injection of Tetrahymena extract. Immunoblots using antibodies against cdc2 showed that injection of Tetrahymena extract induced fast mobility of the recipient cdc2 in the presence of the recipient protein synthesis. The same mobility shift of the cdc2 was also induced when M‐phase‐promoting factor containing Xenopus oocyte extract was injected into immature oocytes or when the immature oocyte extract was treated with alkaline phosphatase. These results indicate that meiosis‐reinitiation‐inducing factor of Tetrahymena functions upstream of M‐phase‐promoting factor to induce dephosphorylation of the recipient cdc2. Tetrahymena cdc2 homologues also showed fast mobility when the Tetrahymena extract was treated with alkaline phosphatase. Preliminary experiments showed that the meiosis‐reinitiation‐inducing factor of Tetrahymena was a soluble protein.